Integrated circuits that incorporate processors and the such typically include some type of data conversion function. This data conversion function can either be in the form of an analog-to-digital converter or a digital-to-analog converter. In the case of the analog-to-digital converter (ADC), analog data is received on an input, sampled and the sample converted to a digital value. Each sample of the analog input signal that is converted is performed during a "conversion" cycle.
One type of ADC that is typically implemented in a processor-based system (these processor-based systems are typically referred to as a "system on a chip") is a successive approximation converter. In the successive approximation converter, a digital-to-analog converter (DAC) is utilized to take a predefined sample output digital word and covert it to an analog value and then compare the generated analog value with the externally generated input voltage level. Each bit of the output digital word in the DAC has associated therewith a capacitor, which capacitors are binary weighted; that is, for the MSB, the capacitor is at a first value and for the next and successive bit, the capacitor is one-half that value, such that each successive bit halves the value of the previous capacitor value, the smallest being, associated with the LSB. The value of the output digital word is continually chanced to determine which combination of capacitors will result in a analog value output from the DAC substantially equal to the level of the input voltage.
One problem with ADCs when utilized in conjunction with significantly larger processing circuits is the sharing of a common clock. This can result in noise problems due to the fact that most sampling operations or conversion operations are initiated at a clock's edge. The noise that occurs at a clock's edge is due to various other processes or logic operations that are triggered from this edge. When dealing with small values of the capacitance, this noise can affect the actual analog output of the DAC that is embedded within the ADC.